Electronic or electromagnetic valve actuation (EVA) systems can be used in internal combustion engines to provide increased flexibility in terms of valve timing and/or lift, rather than being constrained by camshaft actuation. Such systems commonly include an electromagnetic actuator coil, which is energized with a current to generate an electromotive force for moving the valve and holding it in a desired position.
Existing EVA systems have certain disadvantages, depending on the setting in which they are used. One disadvantage relates to the need to provide a circulation path for freewheel current generated by the actuator coil after being energized (e.g., through application of a supply voltage). Typically, providing a circulation path for freewheel current requires multiple. switches and other components for each actuator coil, which increases manufacturing costs. For example, prior systems have employed a half bridge topology to allow for freewheel current circulation. The half bridge topology allows freewheel current from an actuator coil to flow through two freewheel diodes into a power bridge bus. To energize actuator coils and provide freewheel current circulation, the half bridge design requires two discrete MOSFET switches and two discrete diodes per actuator coil, for every coil. Another disadvantage is that many existing systems are inefficient in their inability to make use of the energy dissipated through freewheel currents.
The above disadvantages may be overcome by the system of the present description, which according to one aspect, comprises: a system for electronically actuating valves in an engine. The system includes a first voltage source, a second voltage source, and plural valve actuator subsystems coupled between the first voltage source and the second voltage source. Each valve actuator subsystem has a valve actuator and a switch. The system also includes a dissipation switch operatively coupled with the valve actuator subsystems, the dissipation switch being selectively operable to control dissipation of energy from any of the valve actuators.
In this way, it may be possible to reduce the number of switches per coil, while also providing faster coil turn-off and meeting the demand of valve actuators operating in the context of internal combustion engines.